f.4 phys,,

(a) v = 0 m/s, t = 22 s, s = 33 m, a = ?
using the equation of motion: s = vt - (1/2).a.t^2
33 = (0).(22) - (1/2)(a)(22x22)
i.e. a = -33x2/(22x22) m/s = -0.1364 m/s2

(b) The total travelling time of the ball is 22 s, hence at 10s after the ball starts to roll, it takes a further (22-10) s = 12 s to travel before coming to rest.

Hence, v = 0 m/s, t = 12s, a = - 0.1364 m/s2, u = ?
use the equation of motion: v = u + a.t
0 = u + (-0.1364)x(12)
i.e. u = 1.6368 m/s

[Note: the post above used a wrong equation because u, the initial velocity, is not zero]

There is a mistaken made by seiya_nt03
For part a, we set up v = u + at and v^2 = u^2 + 2as
We get a = -0.136 ms^-2, u = 3 ms^-1

For part b, Apply v = u + at
v = 3 + (-0.136)(10)
v = 1.64 ms^-1

2008-10-07 20:05:34 補充：
mistake, not mistaken

A soccer ball is initially at rest on a flat playground. At time t=0, a kid kicks on the ball and the ball rolls in a straight line. The ball finally comes to stop at time t=22s after travelling a distance of 33m.

a) Find the average deceleration of the ball.

s = ut +1/2 (t^2)a
33 = 0 +1/2 (22^2)a
a = 0.136 m/s^2


b) What is the speed of the ball at t=10s?

v = u + at
v = 0 + 0.136＊10
v = 1.36 m/s